Various embodiment of the invention relate generally to a signal quantizer and particularly to a signal quantizer with a regenerative gain.
A limitation of prior-art oversampled analog-to-digital converters is that they may take a significant number of samples to produce a high-resolution estimate of an input signal. For example, a sigma-delta modulator that is effectively an analog-to-digital converter and whose loop filter has only a single integrator and whose comparator is a 1-bit comparator may require approximately 2N samples to produce an estimate with N-bits of resolution. Accordingly, a 12-bit estimate may require on the order of 4,096 samples or more. The large number of samples required leads to a large latency.
The foregoing limitation may be partially overcome by the use of more integrators in the loop filter of a sigma-delta modulator. The order of a modulator refers to the number of integrators used in a modulator. It can be shown that a second-order, single-bit modulator achieving 12-bit resolution estimates may require on the order of 90 clock cycles.
Unfortunately, the use of a higher modulator orders entails stability problems on account of the use of feedback in the modulator. Alternative approaches use multiple modulators cascaded together to achieve higher order thus better resolution, but this is at the cost of increased system complexity, die area and power consumption.
Sensors are readily used for a multitude of applications, many of which employ sensors operating in a duty-cycled mode. In such a mode, a sensor wakes up, makes a measurement and goes back to sleep. During its active state, or while not asleep, such a sensor consumes power. Inasmuch as low-power operation is a desirable feature for a sensor, it would be useful to complete a measurement in the shortest possible timeframe.
Many sensors are capable of producing a digital reading corresponding to the sensor output. Such sensors may include one or more analog-to-digital converters (ADCs) which are devices responsible for measuring a continuous quantity such as voltage, current, or charge and producing a numerical, digital output proportional to that voltage, current or charge. In some applications, sensors generate outputs that may represent the physical quantity being measured in terms of voltage, current or charge. Therefore, by combining a sensor with an analog-to-digital converter, a sensor may be capable of representing a quantity to be sensed with a digital number and provide that number as an output.
For example, a temperature sensor may measure temperature by first representing the temperature as a voltage, current or charge. Subsequently, that voltage, current or charge may be applied to an ADC to produce a digital output. By such an arrangement, a digital temperature sensor is formed.
As in temperature sensing, many other sensor applications may require high resolution and low-power operation. There is thus a need of a signal quantizer achieving high resolution within a short timeframe so that measurement time and therefore power consumption are minimized.